Modern sushi was initially created in Japan in the early 1800's. There are many different types of sushi made and consumed in Japan and other Asian countries as well as types of sushi popular in the Americas and Europe. Cooked, vinegared rice is a common ingredient to all of the different types of sushi. In Japanese sushi, the cooked vinegared rice is prepared from white, short-grain Japanese rice mixed with rice vinegar, sugar, and salt. It is generally cooled to room temperature following cooking and then combined with additional ingredients, including nori black seaweed wrappers, various types of seafood, various types of vegetables, and other ingredients. While all of these ingredients contribute to the taste and texture of sushi, the taste and texture of sushi rice is often a significant contributor or the main contributor to the overall perception, to sushi consumers, of the quality and freshness of sushi products.
As sushi has become more and more popular around the world, and as the demand for sushi has correspondingly increased, attempts have been made to prepare frozen sushi products in order to achieve the same mass-production and mass-distribution efficiencies as obtained with other frozen, processed food products. Many of the ingredients in sushi can be successfully frozen and subsequently thawed without significantly degrading their taste and texture. However, until the development of the processes and systems to which the current document is directed, there has been no satisfactory method for freezing sushi rice. The taste and texture of rice significantly degrades while the rice is frozen and refrigerated, rendering thawed, thawed and refrigerated, and heated frozen sushi unsatisfactory to sushi consumers. The degradation of sushi rice is particularly prevalent in commercial environments, in which frozen-storage and refrigeration units often fail to maintain constant temperatures, leading to fluctuating temperatures, fluctuating humidity, and even to multiple unintended freeze/thaw cycles.